Help diagnosing problem

[SayHiToRambo]

08 trooper 1100

Bit of background. First the machine would take for ever to start. So I adjusted the valve shims into spec and made sure the timing is correct. Starts perfectly now. 
 

now it fluctuates on idle. Bogs down, Revs up, repeat. I noticed the fuel pressure drops from 60psi to 20psi while that happens. It also bogs down at the lower end of each gear, higher rpm seems to be fine. Seems to struggle under load. In neutral it revs up perfectly. 
 

brand new fuel pump, fuel filter, gas. I noticed on the fuel pressure regulator there’s that vacuum nipple, it’s not attached to anything and I’m not sure where it would go. Possibly the problem? 
 

Another issue is the tip off the end of the exhaust is broken off, sensor is still attached and connected. Could that cause these issues? 
 

my next plan was to look into the pressure regulator and voltage to fuel pump while driving. Is there anything I’m missing or any ideas you guys have? 
 

thanks! 

[Dan B]

Difficult to troubleshoot remotely.  Things I might check.  Take a look at the ignition system.  When an engine is under load, the ignition system can breakdown.  The fuel pressure dropping to 20psi makes me wonder why.  It's an elecric pump and unless the voltage drops, it should maintain 50psi per the specs.  That port may be a port to measure fuel rail pressure.  But you could have a vacuum leak in the iintake manifold or the ductwork to the air filter.

[SayHiToRambo]

9 hours ago, Dan B said:

Difficult to troubleshoot remotely.  Things I might check.  Take a look at the ignition system.  When an engine is under load, the ignition system can breakdown.  The fuel pressure dropping to 20psi makes me wonder why.  It's an elecric pump and unless the voltage drops, it should maintain 50psi per the specs.  That port may be a port to measure fuel rail pressure.  But you could have a vacuum leak in the iintake manifold or the ductwork to the air filter.

Update. Fuel pump is good, no voltage drop. I removed the cat thinking it was plugged. Almost completely solved the bogging issue. 
 

I cleaned out the fuel pressure regulator. No abnormalities. Machine has fire coming out the exhaust when full throttle. Must be running lean. I upped the fuel pressure to 75psi from 60psi and it ran even better, flames out the back were noticeably less. Can’t adjust the regulator any higher. 
 

im thinking new injectors. 
 

anyone agree or have other ideas? 
 

thanks! 

[Jhen]

How fast is the pressure drop when you shut off the engine.  If it drops too quickly, it may be a bad injector, or pressure regulator.

[Ben1098]

Don't know your machine  BUT you described the broken off exhaust pipe tip  "with the sensor still attached and connected".  This have 4 wires and looks like an O2 sensor?  If so, your ECM doesn't know the fuel air ratio (amount of O2 in the exhaust) with it reading open air O2 content and mapping to the wrong injection pulse width (amount of fuel).  That said.....reattach the tip and seal  good enough so that no free air (O2) enters downstream before the O2? sensor.  Might want to undo the fuel pressure bump up and check again.  Some of the different O2 sensor vendors for the HiSun variants had problems......e.g.    2 hole vs 3 hole and had erratic runability problems with everything else working AOK.  Even had some new junkers right out of the bag.

[SayHiToRambo]

On 1/7/2025 at 7:52 AM, Jhen said:

How fast is the pressure drop when you shut off the engine.  If it drops too quickly, it may be a bad injector, or pressure regulator.

It drops very slowly. Maybe 10psi every 30 seconds. I’m hoping it’s not injectors because I can’t find them anywhere. Only place is eBay and it’s $150 USD each. 

[SayHiToRambo]

21 hours ago, Ben1098 said:

Don't know your machine  BUT you described the broken off exhaust pipe tip  "with the sensor still attached and connected".  This have 4 wires and looks like an O2 sensor?  If so, your ECM doesn't know the fuel air ratio (amount of O2 in the exhaust) with it reading open air O2 content and mapping to the wrong injection pulse width (amount of fuel).  That said.....reattach the tip and seal  good enough so that no free air (O2) enters downstream before the O2? sensor.  Might want to undo the fuel pressure bump up and check again.  Some of the different O2 sensor vendors for the HiSun variants had problems......e.g.    2 hole vs 3 hole and had erratic runability problems with everything else working AOK.  Even had some new junkers right out of the bag.

Yes that’s correct, it’s the sensor after the cat. The one before the cat is still there. I’m planning on putting it back and trying that. 
 

these are my current symptoms and it has me stumped. I’m starting to think it’s electrical. At idle engine rpm’s raise and lower every couple of seconds, when driving 1st gear runs great until the higher rpm’s then it bogs. 2nd can run pretty great until higher rpm’s then it bogs. Sometimes it runs great tho. 3rd gear is almost a no go unless I’m high on the speed and throttle. 
 

I’ll attach the exhaust sensor and let you know. If you guys have any other ideas or want more details about the machine from me please let me know. I’m running out of ideas.

thank you! 

 

[SayHiToRambo]

Update. Problem has been solved. Fuel line from tank - filter - pump was too long. Shortened it and 95% of the issue was fixed. 

[Dan B]

??? Wow!  I'd have never thought about that.  Maybe there was a restriction in the section of the fuel line that you removed.  Things are looking up!